Nitric oxide (NO) is a small, gaseous free radical molecule that can mediate cellular signaling that is critical for the proper functioning of the vascular, immune and nervous systems. Within the nervous system, its ability to cross cell membranes and mediate communication between cells in the absence of specialized synaptic machinery gives it a power and flexibility not possible for conventional neurotransmitters. High levels of nitric oxide synthase (the enzyme that generates NO) expression has led to the hypothesis that NO mediates and/or modulates signaling within the primary olfactory neuropil. This idea has been strengthened by the observation that the hallmark spheroidal structures within the primary olfactory neuropil could be ideal to regulate the diffusion of a small molecule such as NO. This proposal takes advantage of the relative simplicity, but parallel organization of an insect olfactory system to investigate the function of NO signaling within the primary olfactory neuropil. We will investigate the production, diffusion, and function of NO within the olfactory system. This will be done by applying the talents of a group of expert researchers to complete the following three specific aims: (1) Characterize odor-induced NO production and diffusion within the AL. (2) Characterize the functional roles of NO signaling in AL neurons. (3) Characterize the behavioral consequences of interfering with NO signaling in the AL. The successful completion of these specific aims will result in a very detailed understanding of the role of NO in the function of this model olfactory system. This understanding will yield insight into the function of this important signaling system in other organisms including humans. In addition, these insights will likely serve as the basis for other experiments designed to examine the role of this very important signaling molecule both in other olfactory systems and in the nervous system in general.